E. Background. A decision was made at the time The FOM was revised to
incorporate all policies and procedures of a non-technical nature into that
manual. When the FOM was published, numerous changes were made to existing
health policy. These changes made the procedural sections of the instruction
obsolete. To avoid confusion for directives users, it has become necessary
to remove inapplicable sections from the instruction. The remainder of the
instruction is still in effect until the directive has been totally revised
and reprinted at a later date.

(a) Mechanical. Because mercury is a liquid at low
temperatures with no tendency to wet glass, it is widely used in scientific
Instruments such as thermometers and barometers. Mercury is also used in the
pressure gauges of vacuum pumps. Potential mercury exposure is a problem not
only in the production of such instruments, but also in research institutions
where such instruments are used extensively.

(b) Electrical. Mercury's very high level of electrical
conductivity lends itself to use in electrical appliances. The principal use
of mercury in this category is for batteries. Mercury is also used in
rectifiers, oscillators, power control switches, and vapor
lamps.

Mercuric oxide is used extensively in dry cells. In such
a battery, the depolarizer is composed of mercuric oxide, the electrolyte is
a strongly alkaline solution of potassium hydroxide saturated with potassium
zincate, and the anode is of zinc. In the manufacture of these cells,
processes such as mixing, blending, and tableting of the mercury present
potential exposure problems. The exposure may be to mercury dust or
vapor.

(c) Chlorine. The chlor alkali process uses saturated and
heated salt brine (25% NaCl in water) to produce Cl2 (chlorine gas), H2
(hydrogen); and NaOH (sodium hydroxide) by electrolysis. The two basic cell
types are diaphragm cells and the mercury cells. Several different designs
in each cell type can be found. Low-voltage, high-amperage power is used in
both types. The cells are usually hooked up in series. Diaphragm cell
construction materials include asbestos, lead, concrete, stoneware, and
possibly Fiberglas. Diaphragm cells do not contain mercury. The mercury
cell uses mercury in a two-chamber system: in the first (electrolyzing)
chamber, chlorine gas is produced and the sodium ion is amalgamated in the
mercury. In the second (denuding) chamber, hydrogen is formed when the
amalgam contacts water and the sodium ions combine with the remaining
hydroxyl ion (OH-) to form NaOH. The basic process reaction for the
electrolytic cells is

Na+ + Cl- + H+ + OH- = Na+ + 1/2Cl2 + 1/2H2 + OH-

In this process the NaOH is extremely corrosive and
mercury leaks, spillage, and recovery are always a problem. As the cells age
and become inefficient, they have to be rebuilt. Rebuilding is a routine
operation in chlor alkali plants, where cells are operated in batteries of
tens and even hundreds. During the rebuilding process, the cells are leveled
off, exposing the mercury surface, creating a potential exposure
problem.

(d) Paint. In the paint industry, mercury is commonly used
in its organic form. In the primary paint industry, however, mercury may
initially be in its elemental form, even though the final product may be
organic. In such primary manufacture, there may be some potential mercury
exposure.

(e) Medicinals. Mercury is used primarily in dental supply
and equipment. Dentists have a variety of uses for mercury, the primary one
being a filler for cavities. Due to mercury's use in medical equipment and
supplies, dental schools and offices and hospitals are sites of potential
exposure.

(2) Signs and Symptoms of Intoxication. Intoxication may
occur in workers excessively exposed to mercury or to its compounds. The
exposure may be due to mercury vapor, mist, dust, or fume, by inhalation,
ingestion, or through skin.

Two general types of mercury intoxication exist, chronic and
acute. Chronic mercury intoxication is caused by exposure to a low
concentration of mercury over an extended period of time. Acute mercury
intoxication is due to a greater exposure and is unrelated to time factors.
Definite symptoms of chronic mercurialism may not appear until after six
months of exposure, or longer. The symptoms are primarily of the nervous and
digestive systems.

The symptoms of overexposure to mercury may include such
personality manifestations as: irritability, excitability, or excessive
timidness. Other symptoms include: headaches, drowsiness or insomnia, and
weakness. Many cases also include reports of sore mouths, excessive
salivation, and perspiration. In mercury intoxication, a common symptom is a
tremor which is aggravated by emotion or excitement. Also included in the
literature as symptoms of mercury intoxication are: loss of appetite,
weakness, digestive disorders, kidney damage, and bleeding
gums.

If an inspector is unfamiliar with the biological monitoring
methods used for mercury, he or she should check with his Senior Industrial
Hygienist. When evaluating biological symptoms, trends within groups of
employees should be noted. Elevation in mercury levels within a group is
often a more significant finding than elevations in an individual because it
indicates a common source.

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